1. Field of the Invention
The present invention relates, according in a general aspect, to the manufacture of tires.
2. Description of the Related Art
As is known, for the industrial manufacture of a tire various semifinished products are assembled together to form a single-piece structure, said products including a carcass ply, at least one pair of annular cores for reinforcing the beads, usually called bead cores, a belt structure, a pair of side-walls, a tread band and a plurality of other reinforcing or filling components which confer to the whole structure a predefined geometry as well as a predefined dimensions and all the mechanical-strength and all the qualitative characteristics which are necessary for a good performance of the tire on the road.
Some of these semifinished products consist of rubber strips having different width and thickness depending on the circumstances; in order to use them during the industrial production of the tires, they are arranged in special storage coils, wound as a continuous strip having a length equal to a multiple of the length necessary for a tire.
An example which illustrates this state of the art is described in British Patent No. 1,495,803 in the name of the Goodyear Tire and Rubber Company.
This patent, which was published in 1977, describes how, for the manufacture and the subsequent application of the components referred to above, the rubber strips supplied by a drawing machine or other production machine, are arranged on top of a thin fabric support belt unwound from a respective coil.
The use of this support belt, or other textile support, is necessary owing to the fact that the unprocessed rubber, in particular when it is still hot, is made of a plastic material which is highly deformable when subject to any type of stress and is therefore unable to withstand the pulling force which is necessary for feeding the belt to the tire forming machine: the main purpose of this belt is precisely that of withstanding this pulling force, protecting the semifinished product from unacceptable deformations.
The thin belt and the strip placed on it are then rolled up together so as to form a storage coil which will be used, during the production of the tires, to supply the required component to the abovementioned forming machines.
In this way the turns of each rolled-up rubber strip are separated from each other by the support belt, thereby avoiding the risk of becoming attached to each other: indeed, if the unprocessed rubber, soon after production, were rolled up into the coil without the presence of the belt, the wound turns would inevitably tend to adhere to each other, making it extremely difficult, if not even impossible, to separate them from each other and in any case subjecting the semifinished product to a pulling force which would change in an unacceptable manner the geometrical dimensions thereof, as well as the characteristics of homogeneity and uniformity.
The simple belt considered in the British patent cited above is not, however, entirely satisfactory: indeed, it cannot prevent compression of the rubber strip in the packing coil, owing to the weight which bears on the wound turns.
For this reason a special belt for supporting the rubber strips is currently known, as shown in FIG. 1.
As can be seen from the drawing, the belt 1 consists of a thin central band 2 of flexible material (for example that commercially known as xe2x80x9cMylarxe2x80x9d), on the edges thereof the linear elements 3, 4, 5 and 6 are provided.
The latter essentially consist of reinforcing rims made of suitable materials, for example expanded elastomer material of suitable thickness, and have V-shaped incisions transversely cut so as to form basically a series of blocks 3a, 3b, 3c, 4a, 4b, 4c, etc.; in this way the belt is provided with the necessary flexibility so that it may be wound up on itself.
The linear elements 3-6 support the central band 2 on which the strip S of a component for the manufacture of tires (shown in broken lines in FIG. 1) is placed and serve as spacers between the various turns of the packing coil, when the belt 1 is wound together with the strip S.
This, obviously, provided that the thickness of the strip S is less than that of each pair of juxtaposed linear elements 3-6 in the winding.
In this connection, it must be noted how the flat configuration of the linear elements 3-6 ensures stable seating of the various turns, also in the case of relative displacement thereof in an axial direction with respect to the coil (caused for example by shocks or the like); this aspect will emerge more clearly from the description of the invention which follows further below.
There are, however, certain drawbacks associated with the known support belts of the type considered above.
Firstly it should be pointed out that the repeated belt winding and unwinding cycles may result in breakage, due to fatigue, of the central band 2 and in particular of the linear elements 3-6; indeed the materials from which these elements are made and referred to above, generally have a limited strength and in the long run are subject to breakage owing to the continuous mechanical stresses, in particular bending stresses, to which they are subject.
Secondly it must be pointed out that, owing to the limited bending strength of the aforementioned materials, it is not possible to wind the belt 1 with a radius below a certain limit value; consequently, the packagings obtained are generally bulky and in particular have the same dimensions both when they are full or empty.
In other words, since the thickness of the belt 1 is determined by that of the linear elements 3-6 and is therefore constant because the latter are made of semi-rigid material, the belt winding in the coil has the same dimensions, irrespective as to whether the strip S is present or not inside it.
This means that, also from a handling point of view, these coil packagings are disadvantageous because they occupy the same space when they are fill and when they are empty.
The Applicant has found that this state of the art may be overcome using a belt for storing semifinished products in the form of rubber strips used for the manufacture of tyres, comprising a central band for supporting the semifinished product, which is provided along its edges with spacing elements having a variable configuration.
According to a first aspect thereof, the invention relates to a belt for storing strip-shaped semifinished products, comprising a central support band along the edges thereof inflatable elements, in particular tubular air chambers, are arranged.
In accordance with a preferred embodiment of the invention, these air chambers have a configuration which has an upper face and a lower face substantially parallel to the central band.
According to a further aspect thereof, the invention also relates to a method and an apparatus for using the belt above, whose features are described further below and summarised in the claims which will follow.